A couple of things, a JD 2640 was 70 hp with 276 ci engine. Watched a neighbor with a 3020 diesel with small 2 row cut and blow and it had a hard time running it (hay or corn). Another neighbor tried his JD 3800 on an IH 784 tractor and lacked power to move out of lowest gear. He made sure he got his 856 diesel up and going ASAP. Cutterhead on a 900 is designed for 3 row capacity along with the drive line. Takes more power to spin that (even no load) than a NH 790, JD 3950, etc. You MIGHT get the 2640 to run it, but you will be disappointed with minimal productivity. If you have a choice in this, I would look at going up more hp or find a smaller chopper in that order.

I nver found that there was much difference in starting power requirement between the 3940/50 and 3960/70 Deere's which are equivelant to the 790 and 900 respectively. In Deere's case I think there's only about 200 pounds difference between those models.The worst thing I found was slugging them. There's ~20% less throat on the smaller machines so when the rolls go full up the smaller tractor just can't pull the slug through on the big machine. Granted, 70 hp won't handle a slug on the 790 either.Capacity would be very, very limited.

Yes, the difference in start up load would be minimal (2-3 hp maybe). That 2-3 hp a lot of times can be critical if the tractor is operating in tough conditions already and you hit a heavy spot, it may make the tractor stall. I was just trying to point out that machines have some degree of power utilization even when no material is being processed.

Better back the pump stops out first then...I run a 3970 Deere harvester (the equivelant of the 900) on a Ford 7710 turned to 105 HP and it works her HARD... with half the knives. Full set of knives is doable but it's extremly hard.The 2640 has nowhere, and I mean nowhere near the power or torque of a 7710.I'm thinking it's about 70 horse? 4 holer, 239 and no turbo?

You'd get by with it in low gear, in a light crop with half the knives and that's about it. As they used to say about driving a Detroit... get in, sit in the seat, slam your hand in the door and drive it like ya hate... cause you're gonna have to hate her to make her chop silage.You best cover the clutch pedal too so you can stop quick when it starts to plug... or get the rolls stopped quick before she goes down for the count. 2400 to 0 happens in about 3 seconds.

It happened in about .003 seconds to our Oliver 1755 a while back. We had our old Fox hooked up and we were chopping brush and other crap with it around the yard. Dad threw in a fork full of stuff that was in a pile and there just so happened to be a 1/2" steel rod mixed in there.

It broke a knife bolt and did a number on it. It twisted the PTO shaft on the chopper as well. We got a new shaft from the junk yard, replaced the junk knives with some other worn out knives we had around.

Didn't run it too much longer after that before we replaced it with our 3000.

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